Abstract: A defect size measurement method based on X-ray digital imaging is proposed. Based on the half-wave height method and taking the dimension measurement error under the half-wave height method as the reference, X-ray digital imaging testing was carried out on the specimens with different slot sizes under the same testing conditions. The total ambiguity value under the same testing conditions was calculated, and the relationship between the ratio of defect size to total ambiguity and the ratio of wave height was summarized. The method was verified by the test. The results showed that the method was simple and practical and could provide technical support for accurate measurement of defect size.